The purpose of radio resource management (RRM) in wireless communication systems is to efficiently manage the use of resources over the air interface (i.e., radio resources). Intelligent management of radio resources is essential for maximizing the air interface capacity, ensuring connection reliability and network stability and reducing the battery consumption of wireless transmit/receive units (WTRUs).
Typical RRM functions include: (1) call admission control, which accepts or rejects requests for new radio links based on the system load and quality targets; (2) handover control, which ensures that a call (connection) is not dropped when a WTRU moves from the coverage area of one cell to the coverage area of another cell; (3) power control, which maintains interference levels at a minimum while providing acceptable link quality; (4) radio link maintenance, which ensures that quality of service requirements for individual radio links are satisfied; and (5) congestion control, which maintains network stability in periods of high congestion.
RRM functions are triggered, and make decisions, based upon a variety of inputs. Among these inputs, air interface measurements observed by the WTRU and the Node B are extensively used. Air interface measurements can originate from either the WTRU or the Node B. WTRU measurements and radio link specific Node B measurements are referred to as dedicated measurements. Cell-specific Node B measurements are referred to as common measurements. Both types of measurements are employed to precisely evaluate the current state of the radio environment. For example, interference measurements can be used to decide the allocation of physical resources in a timeslot or frequency band.
Typical measurements which RRM functions rely upon for evaluating the status of the radio environment include: interference signal code power (ISCP); received power measurements (both individual radio link and received total wideband power (RTWP)); received signal strength indicator (RSSI); transmission power, (including individual radio link power and total power); and signal-to-interference ratio (SIR) measurements. These measurements are just several examples of the many measurements that are applicable with the proposed invention.
As will be described hereinafter, some of these measurements may be predicted and a combination of their latest reports and their predictions may be used when the system is in a transient phase.
Unfortunately, there is a drawback in the manner in which current RRM functions are performed. There are several conditions that may cause the aforementioned measurements to be unavailable or invalid. First, it is possible that measurements are simply not reported, or measurement reports are corrupted over the air interface. For example, WTRU measurement reports are eventually encapsulated into transport blocks (TBs) to which cyclic redundancy check (CRC) bits are attached. The Node B physical layer determines whether an error occurred by examining the CRC bits. In the event of an error, the Node B physical layer may either deliver the erroneous TB to upper layers with an error indication, or simply indicate to upper layers that an erroneous TB was received on a particular transport channel or a set of transport channels. Such a scenario is particularly relevant when considering WTRU measurements since they are sent over the air interface.
Secondly, measurements generally have an age threshold, after which the measurement is considered invalid. If measurement reports are not frequent enough, it is possible that valid measurements will eventually become invalid, and thus unavailable to RRM functions.
Finally, it is possible that measurements are simply invalid because the radio link or the system has entered a transient phase that is undergoing stabilization. For example, interference measurements are unstable for a certain period of time (up to ½ second) following the configuration or reconfiguration of a radio link due to the transient phase of the power control. Such measurements should not be used to trigger RRM functions or to make decisions since the current state of the radio link or the system is unstable.
Accordingly, an improved system and method for obtaining measurements for more effective radio resource management is needed.